The relative softness of the balata cover is particularly advantageous in that a relatively experienced golfer can apply a spin to a balata-covered ball to control the ball in flight to produce a draw or a fade, or a backspin to cause the ball to "bite" or stop abruptly on contact with the green. Such playability is particularly important in short iron play where accuracy overrides distance considerations, and is exploited significantly by the more highly skilled players.
However, golf balls utilizing balata-based compositions as the covering are also quite susceptible to being cut easily if mis-hit and therefore such golf balls have a relatively short life span.
Due to this negative property, balata and it's synthetic substitutes, trans-polybutadiene and trans-polyisoprene, have today been essentially replaced by new cover materials, primarily by a copolymer of ethylene and methacrylic acid, sold by E. I. DuPont de Nemours and Company under the trademark SURLYN. Neutralization of a number of the acidic functional groups, generally on the order of from about 18 to about 73 percent, is effected with metal ions, such as zinc or sodium, producing a thermoplastic which has several advantages over balata when employed as the cover material for golf balls.
In addition to cost-saving and ready availability vis-a-vis balata, the properties of SURLYN may be controlled and varied to produce golf balls having different playing characteristics and properties which may be controlled and varied in hardness, cut resistance, shear resistance, and resilience. These properties can be varied by selection of suitable ethylene-methacrylic acid ratios, degree of neutralization and the particular metal ion employed.
While the use of SURLYN salts of poly(ethylene-methacrylic acid) copolymers as golf ball covers has been a major factor in the production of two-piece balls which for all practical purposes cannot be cut in play and which travel further when hit than any other USGA regulation ball as measured by controlled tests, the coefficient of restitution exhibited is an extremely important factor, with increased values resulting in increased distances which the ball will travel.
The golfing industry has therefor attempted for a numbers of years to develop a cover composition which possesses both the durability of the SURLYN salts of poly(ethylene-methacrylic copolymer) and increased coefficients of restitution.
It is therefore an object of the present invention to provide a golf ball which is resistant to cutting during play and which exhibits a markedly elevated coefficient of restitution.
It is another object of the invention to provide a golf ball which is longer, i.e., which does not have a distance shortcoming when struck with a golf club.
A further object of the present invention is to provide a golf ball which exhibits a bright white coloration and which does not yellow upon aging.
Still another object is to provide a golf ball cover composition which can be easily processed.